Method and apparatus for dying pulpy slurries

ABSTRACT

A method and apparatus for drying pulpy slurries. By way of a rotary sprayer, the pulpy slurry is sprayed in the form of droplets horizontally toward a wall which surrounds the sprayer, while a stream of drying gas is directed upwardly through the space between the wall and the sprayer to carry upwardly into a drying chamber droplets of slurry which are smaller than a given magnitude and which flow concurrently with the drying gas to be dried thereby. Droplets which are larger than this magnitude strike against and cling to the wall so that they can subsequently be removed therefrom to be delivered again to the sprayer.

United States Patent Mullner 3,l75,686 3/1965 Rieth 34/8 X Primary Examiner-John J. Camby [75] Inventor: Wilhelm Mullner, Wien-Mauer,

Austria Attorney-Harold D. Steinberg et a1' [73] Assignee: Waagner-Biro A.G., Vienna, Austria I I 57 ABSTRACT [22] Filed: July 3, 1972 A method and apparatus for drying pulpy slurries. By {211 App! 26866o way of a rotary sprayer, the pulpy slurry is sprayed in the form of droplets horizontally toward a wall which [30] Foreign Application Priorit Dat surrounds the sprayer, while a stream of drying gas is July 6 1971 Austria A 5854/71 directed upwardly hmugh the Space between i and the sprayer to carry upwardly into a drying cham- 52 us. Cl. 34/8 34/10' dmplets Slurry which are smaller than a give" 511 Im. Cl F26 b 5/08 magnitude and which concurrently with the drying [58] Field of Search 34/8 58 10 57 E gas be dried thereby-13mph whih are larger than this magnitude strike against and cling to the wall so {56] References Cited that they can subsequently be removed therefrom to be UNITED STATES PATENTS delivered again to the sprayer. 2,561,392 7/1951 Marshall 34/10 I 17 Claims, 2 Drawing Figures I I. i l l l I I PATENTEDHBT 2 m5 SHEET 1 [IF 2 Fig.1

METHOD AND APPARATUS FOR DYING PULPY SLURRIES BACKGROUND OF THE INVENTION The present invention relates to drying methods and apparatus.

In particular, the present invention relates to a method and apparatus for drying pulpy slurries.

It is already known to dry pulpy slurries by utilizing a drying tower in which the pulpy slurry is sprayed with droplets flowing concurrently with a drying gas in the tower.

According to the known methods and apparatus, the size of the drying tower is determined on the basis of the largest particles which are to be dried. Thus, the conventional towers must be made large enough to be able to dry the largest particles which are encountered. Therefore, the conventional towers are extremely large, particularly in the case where the pulpy slurries which are to be dried have a high water content. In addition, these conventional structures require expensive preparation installations so that the size of the droplets of the pulpy slurry can be maintained as small as possible. If it should happen that there is a deviation beyond the largest droplet size for which the tower is designed, then droplets cling to the inner surface of the tower requiring a time-consuming and tedious cleaning operation to be carried out.

SUMMARY OF THE INVENTION It is accordingly a primary object of the present invention to provide a method and apparatus which will avoid the above drawbacks.

In particular, it is an object of the invention to provide a method and apparatus which enable a continuous drying operation to be carried out in a highly reliable manner.

More particularly, it is an object of the Invention to provide a method and apparatus which will enable the drying gas to function also to classify the droplets according to size so that the drying chamber of the tower will only receive droplets which have a size small enough to be dried efficiently in the tower, while larger droplets which cannot be accommodated in the drying tower are separated from the drying gas stream.

Yet another object of the present invention is to provide amethod and apparatus according to which the slurry which is separated from the gas stream is again prepared and returned to the tower to be dried therein.

Furthermore, it is an object of the present invention to provide an apparatus which is relatively small, inexpensive, and compact.

It is especially an object of the present invention to provide a method and apparatus according to which the droplets which are to be dried are contacted only by a gas which has a laminar flow.

According to the method of the invention the slurry which is to be dried is sprayed in the form of droplets horizontally toward a wall while there is simultaneously directed upwardly across the space through which the droplets are horizontally sprayed a drying gas which carries up into a drying chamber droplets which have a size less than a given magnitude. Thus, the latter droplets will be dried during concurrent flow with the drying gas up into the drying chamber. Those droplets which are of a size greater than the latter magnitude strike against and cling to the wall from which they are removed, and the thus-removed material is again prepared to be sprayed horizontally toward the wall.

With the apparatus of the invention a rotary spray means sprays the slurry in the form of droplets horizontally toward a wall which surrounds and is spaced from the spray means.- Simultaneously a conduit means delivers a drying gas which flows upwardly through the space between the spray means and the wall to carry up into a drying chamber those droplets which are smaller than a given magnitude so that these droplets will be dried during concurrent flow with the drying gas into the drying chamber upwardly beyond the horizontal plane in which the droplets are sprayed by the spray means. The wall against which the larger or heavier particles strike and to which they cling is rotated slowly, and a scraper is situated adjacent the inner surface of the rotary wall to scrape therefrom the slurry which is not carried up into the drying chamber by the drying gas. This removed non-dried material is again prepared for delivery tp the spray means.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:

FIG. 1 is a schematic sectional elevation of one possible apparatus according to the invention for carrying out the method of the invention, the section of FIG. 1 being taken in a vertical plane which contains the central axis of the drying tower; and

FIG. 2 is a schematic sectional elevation of another embodiment of an apparatus according to the invention for carrying out the method of the invention, the section of FIG. 2 also being taken in a vertical plane which contains the central axis of the tower.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1, there is schematically illustrated a drying tower l which has an upper end region terminating in the top wall 18 and a lower end region terminating in the lower annular wall 13. Between these upper and lower end regions the tower has a hollow interior which defines an interior drying chamber 19 which extends between the upper and lower end regions of the tower.

Adjacent the lower end region of the tower there is situated, in communication with the interior drying chamber 19, a rotary spray means 2 which has a central axis coinciding with the central vertical axis of the tower. This rotary spray means 2 is in the form of an atomizer which rotates at high speed and which is driven by way of a drive means 5. This drive means 5 is supported in the interior of a service room 6 which is situated beneath the lower end region of the tower with the drive means 5 being in the form of a suitable motor connected by a chain drive, for example, to the spray means 2 so as to-rotate the latter at a high speed. The pulpy slurry which is to be dried is delivered in an unillustrated manner to an installation 23 in which the slurry is prepared for delivery to the spray means 2, and delivery takes place by way of. the conduit 38 which is shown schematically leading from the installation 23 to the spray means 2. Any suitable pump or the like may be used for pumping the slurry from the installation 23 along the conduit 38 into the spray means 2, and there is located in the interior of the service room 6 controls such as suitable valves and the like connected with the conduit 38 for controlling the flow of slurry to the spray means 2.

The rotary spray means 2 sprays the pulpy slurry in the form of droplets horizontally in the horizontal spray plane 3, and those droplets which are larger than a given magnitude continue to travel in the manner indicated by the arrows 24 toward the inner surface of a cylindrical wall 10 which coaxially surrounds the spray means 2. Thus these relatively heavy and relatively large droplets will strike against and cling to the inner surface of the wall 10.

A conduit means 8, 9 communicates with the space beneath the plane 3 for delivering upwardly through the sprayed droplets a drying gas which flows upwardly into the drying chamber 19 in the manner indicated by the arrows 26. The drying gas which is initially prepared in any suitable way is delivered to the conduit 9 to flow therefrom into the conduit 8 which at its lower portion extends spirally around the service room 6, this conduit 8 having an upper annular portion surrounding the upper end region of the service room 6 where the motor and the spray means 2 are supported, so that the drying gas is delivered in the manner indicated by the arrows 31 to flow upwardly through the droplets so as to carry up into the drying chamber those droplets which have a size less than a given magnitude. Thus, the lighter particles which do not strike against and cling to the wall 10 are carried by the gas stream up into the drying chamber 19 to be dried during concurrent flow with the gas stream.

The finest particles which are to be dried are thus dried during concurrent flow with the gas stream and continue to flow with the gas in the manner indicated by the arrows 28 and 29 out of the drying tower into a separating cyclone 21 where the dried fine particles are separated from the gas in a well known manner. As is indicated by the arrow 30, these fine dried particles are collected from the cyclone 21. For example, at this location the dried fine particles may be received in suitable sacks so that they may be further utilized.

The particles of intermediate size which on the one hand do not strike against and cling to the wall 10 and which on the other hand are not carried out with the gas to the cyclone 21 are sustained by the upwardly flowing current of gas in the interior of the drying chamber 19. These particles of intermediate size remain suspended in the drying gas until they are dry and travel outwardly beyond the upwardly directed stream of gas to fall downwardly into the space surrounding the wall 10, as indicated by the arrows 25. A discharge wall 14 is situated in the path of falling movement of these dried particles, this discharge wall 14 being of an annular configuration and having a flat upwardly directed horizontal surface for receiving the falling dried particles. The wall 14 is fixed at its inner periphery to the exterior surface of the cylindrical wall 10.

The outer upper portion of the wall which defines the conduit means 8 for the drying gas is fixed at its upper edge to the inner edge of the horizontal circular wall 13 which defines the lower end of the drying tower 1. This wall 13 supports at its upper surface rollers which in turn support the wall 14 so that the discharge wall 14 together with the cylindrical wall 10 can rotate as a unit about the central axis of the tower. For this purpose a drive means 17 is provided. Thus the drive means 17 includes a motor situated at the exterior of the tower and directly carried by the wall 13. This motor has a shaft extending through the wall 13 to drive a gear transmission which in turn rotates a friction wheel, for example, which frictionally engages the exterior surface of the wall 10 just beneath the discharge wall 14 so as to rotate the walls 10 and 14 as a single unit slowly around the central axis of the tower. Instead of a friction drive it is of course possible to mount a ring gear on the exterior surface of the wall 10 meshing with the gear train which is driven by the motor of drive means 17.

The embodiment of FIG. 2 differs from that of FIG. 1 only with respect to the drive means for driving the rotary walls 10 and 14. Thus, in the embodiment of FIG. 2 the drive means 17 is situated in the interior of an observation chamber 33 carried by the top wall 18 of the tower directly beneath the latter wall 18. In this observation chamber are located instruments and the like as well as windows through which operators may check on the operation of the drying tower. As is apparent from FIG. 2, the drive means 17 includes a driving motor situated directly in the observation chamber 33 and connected through a suitable gear transmission to a vertically extending drive shaft 40 which is coaxial with the central axis of the tower and which is supported by suitable bearings at the top wall 18 and at the bottom wall of the observation chamber 33. This shaft 40 extends down into the upper region of the rotary wall 10 which in this case has an upper frustoconical portion. The wall 10 is fixed with radiating spokes 41 which are indicated schematically in FIG. 2 and which are fixed at their outer ends to the rotaty wall 10. Thus the wall 10 is fixed through the spokes 41 to the rotary drive shaft 40 to rotate with the latter, and the discharge wall 14, because it is fixed to the wall 10, will also rotate therewith. Therefore in this case the lower end region of the tower 1 is not formed by a horizontal wall portion 13 but instead has the tapering, frustoconical wall portion illustrated in FIG. 2. Except for these differences the embodiment of FIG. 2 is identical with that of FIG. 1.

A gas-flow smoothing means is provided for delivering a laminar flow of drying gas to the particles which are sprayed in the plane 3 by the spray means 2. Therefore, the particles which are to be dried are engaged by a drying gas which does not have any non-linear currents. The illustrated gas-flow smoothing means takes the form of a pair of horizontal plates 4 formed with apertures 20 so that the drying gas when travelling up through the conduit means 8 must flow through the apertures 20 of the walls 4 before reaching the interior space which is surrounded by the wall 10. The apertures of the plates 4 assure an even distribution of the drying gas across the interior of the wall 10 and eliminate non-linear currents so that a laminar flow of the drying gas is achieved in this way. The apertures of the pair of plates 4 have a size and distribution which will not provide a great resistance to the flow of the drying gas. The resistance to flow with this structure is maintained only on the order of approximately five millimeters of water column pressure.

A means 15 is provided for removing the dried particles which are received by the upper surface of the rotary discharge wall 14. This means 15 takes the form of a suitably curved scaper blade or the like fixed to the inner surface of the tower 1 just over the wall 14 and having a lower edge adjacent the top surface of the wall 14. Therefore, as the wall 14 rotates with respect to the stationary removing blade the latter will remove the dried material from the top of the discharge wall 14, and the curvature of the blade 15 is such that it delivers the dried material in the direction indicated by the arrow 34 into a collecting means 16 from which the dried material is removed, for example, through a conduit 32 or the like, so that the dried material can be directed in this way to a location where further use is made of the dried material.

As is indicated by the arrows 24, the heavier and larger particles will strike against and cling to the inner surface of the rotary wall 10. Thus these particles will be fixed temporarily at least to the rotary wall 10 at the inner surface thereof. A means is also provided for removing this material from the inner surface of the wall 10. Thus, according to a further feature of the invention the inner surface of the upper part of the conduit 8,just over the upper apertured plate 4,fixedly carries a scraper 11 which extends axially along the inner surface of the rotary wall 10 so as to scrape from the latter the non-dried droplets which are larger than the magnitude required for the droplets to be carried up into the drying chamber by the drying gas. The non-dried material which is removed in this way by the scraper device 11 falls along a path defined by a pipe into a collecting unit 12 from which the non-dried material is returned to the preparation installation 23 to again flow inthe manner indicated schematically through the conduit 38 back to the spray means 2. Thus, this material is again prepared for drying and is again delivered to the spray means.

As was indicated above, the conduit means 8 for the drying gas has an upper annular portion surrounding the upper end region of the service room 6. This upper annular portion of the conduit means communicates with a spiral portion thereof which extends downwardly and helically around the service room 6 with the lowest part of the conduit means being situated on the right side of the service room 6, as viewed in FIG. 1, where the conduit means 8 communicates with the conduit 9 which delivers the drying gas to the conduit 8. The service room 6 is conveniently provided with an entrance 7 situated at that side of the service room 6 which is directly opposite the lowest part of the conduit means 8, so that in this way it is possible for personnel to enter the service room 6 in the manner indicated schematically by the arrow 22. Thus, the lower part of the conduit means 8 has a spiral portion extending symmetrically about the service room 6 and leaving at the side of the service room 6 which is diametrically opposed to the lowest portion of the conduit means 8 a space for an entrance 7 through which access may be had to the interior of the service room 6.

The observation chamber 33 is defined by a downwardly tapering wall which is fixed to and extends down from the top wall 18 of the tower. This tapered side wall of the observation chamber 33 is surrounded by a frustoconical reinforcing wall which defines with the upper intersection between the vertical and top walls of the tower 1 the chamber 27 which surrounds the upper portion of the observation chamber 33 and which communicates with the cyclone 21. This frustoconical reinforcing wall is formed with apertures through which the gas flows together with the finest particles in the manner indicated by the arrows 28 and 29 into the circular chamber 27 which communicates with the cyclone 21. The apertures in this reinforcing wall through which the gas with the finest particles passes are schematically indicated by the dotted lines in FIGS. 1 and 2. Any suitable suction fan communicates with the chamber 27 for sucking the drying gas into the chamber 27 and delivering it to the cyclone 21.

Thus, it will be seen that with the above-described method and apparatus of the invention the drying gas serves not only to dry the pulpy droplets but also to classify them so that the finest particles of pulpy slurry are drawn off together with the drying gas to be separated therefrom in the cyclone 21 while the major part of the slurry droplets are dried in the drying chamber while suspended in the drying gas until they fall onto the discharge wall 14. Because of the classification action of the drying gas, the heaviest particles which are too large to be suspended in the gas never move upwardly beyond the wall 10 and instead strike against and cling to the wall 10 to be removed therefrom by the removing means 11v so that this removed, non-dried material can again be prepared for reintroduction to the spray means 2, as described above. This combination of classifying and drying action of the drying gas with the method and apparatus of the invention enables the size of the tower to be reduced, while eliminating any possibility of tedious costly cleaning operations.

What is claimed is:

1. In a method of drying a pulpy slurry, the steps of spraying, at a lower region of a drying chamber, droplets of the slurry horizontally toward a wall while directing upwardly through the space across which the droplets are sprayed toward said wall a drying gas which carries into the drying chamber slurry droplets which have a size less than a given magnitude and which are dried during concurrent flow with the drying gas into the drying chamber, those slurry droplets which have a size greater than said given magnitude striking against and clinging to said wall so that only droplets which have a size less than said given magnitude flow with the drying gas into the drying chamber.

2. In a method as recited in claim 1 and including the step of removing from said wall those droplets which strike thereagainst and cling thereto.

3. In a method as recited in claim 2 and wherein the removal of the slurry from the wall is carried out by rotating the wall at a relatively slow speed with respect to a stationary scraper which scrapes the slurry from the wall.

4. In a method as recited in claim 1 and wherein the step of spraying the slurry toward the wall is carried out by rotating at high speed an atomizer to which the slurry is fed to be sprayed by the atomizer toward the wall.

5. In a method as recited in claim 2 and including the step of again preparing the slurry removed from the wall for spraying into the drying chamber and then again spraying the thus-prepared slurry toward the wall.

6. In a method as recited in claim 1 and including the step of receiving dry material from the drying chamber on a moving discharge wall which delivers the dry material from the drying chamber.

7.. In a method as recited in claim 1 and wherein the drying gas stream is introduced in a laminar flow into the drying chamber across the sprayed slurried droplets so that at the location where the latter encounter the entering gas stream the stream is free of any non-linear currents.

8. In an apparatus for drying pulpy slurries, a drying tower having upper and lower end regions and having a hollow interior drying chamber extending between said upper and lower end regions, spray means for spraying the pulpy slurry which is to be dried in the form of droplets horizontally across part of the drying chamber at the lower end region of the tower, conduit means communicating with the drying chamber at the lower end region of the tower for directing upwardly into the drying chamber a drying gas which travels upwardly across the horizontally sprayed droplets to carry droplets which are smaller than a given magnitude upwardly into the drying chamber to be dried during concurrent flow with the drying gas, and gas-flow smoothing means situated in the path of flow of the drying gas into the drying chamber below and adjacent the space through which the droplets are sprayed by the spray means for providing a laminar flow of the drying gas at the location where the latter encounters the sprayed droplets.

9. The combination of claim 8 and wherein said gasflow smoothing means includes a plurality of apertured plates situated one above the other and extending across the gas stream with the latter flowing through apertures of the plates to achieve the laminar gas flow.

10. The combination of claim 8 and wherein a service room is situated beneath the lower end region of the tower, drive means operatively connected with said spray means for driving the latter, said drive means being situated in said service room, and said conduit means extending spirally around said service room up to the lower end region of the tower into communication with the drying chamber so that said conduit means has a lower portion situated on one side of the service room, said service room being formed with an entrance diametrically opposed to said lower portion of said conduit means.

11. The combination of claim 8 and wherein a drive means is operatively connected to said spray means for rotating the latter about a vertical axis, to spray the droplets in a substantially horizontal plane which is normal to said vertical axis, and rotary wall means surrounding said vertical axis and spaced from said spray means to define with the latter a space between said wall means and spray means through which the drying gas flows upwardly into the drying chamber, whereby particles which are greater than said magnitude strike against and cling to said rotary wall means.

12. The combination of claim 11 and wherein a stationary scraper means extends axially along said rotary wall means adjacent an inner surface thereof which is directed toward said spray means for scraping from said rotary wall means those droplets which cling to said rotary wall means, and collecting means situated in the path of movement of the non-dried material scraped from said rotary wall means to receive the nondried material.

13. The combination of claim 11 and wherein a horizontal annular discharge wall is fixed to said rotary wall at an outer surface of the latter which is directed away from said spray means to rotate with said rotary wall, said discharge wall being situated in the path of falling movement of dried particles which flow outwardly beyond the drying gas stream to fall onto and be collected by said discharge wall, stationary removing means situated adjacent the upper surface of said discharge wall for removing dried material therefrom as the discharge wall rotates together with said rotary wall, and collecting means situated in the path of movement of the removed dried material to receive and collect the latter.

14. The combination of claim 8 and wherein said gasflow smoothing means includes a pair of apertured plates situated one above the other and formed with apertures which provide a relatively low resistance to the flow of drying gas on the order of five millimeters of water column pressure, said apertured plates distributing the drying gas uniformly with respect to the space through which the drying gas enters into the drying chamber and across which the particles are sprayed by said spray means.

15. The combination of claim 14 and wherein a service room is situated beneath said lower end region of said tower, said conduit means extending spirally around said service room from a lower region of said conduit means situated at a lower part of said service room up to an upper region of said conduit means which is of an annular configuration and which is covered by said apertured plates, the latter surrounding an upper region of the service room, and said service room having an entrance situated at the elevation of the lower region of said conduit means.

16. The combination of claim 11 and wherein a drive means is operatively connected to said rotary wall means for rotating the latter, said drive means being carried by said tower at said upper end region thereof and including a shaft extending downwardly along and through the drying chamber from said upper end region of the tower, said shaft having a lower portion operatively connected with and carrying said rotary wall means so that the latter rotates with said shaft, said drive means including at the upper end region of said tower a drive connected to said shaft of said drive means for rotating said shaft.

17. The combination of claim 11 and wherein a drive means is operatively connected to said rotary wall means for rotating the latter, said drive means being situated at the elevation of the horizontally sprayed particles and including a driving motor carried by but situated at the exterior of the tower. 

1. In a method of drying a pulpy slurry, the steps of spraying, at a lower region of a drying chamber, droplets of the slurry horizontally toward a wall while directing upwardly through the space across which the droplets are sprayed toward said wall a drying gas which carries into the drying chamber slurry droplets which have a size less than a given magnituDe and which are dried during concurrent flow with the drying gas into the drying chamber, those slurry droplets which have a size greater than said given magnitude striking against and clinging to said wall so that only droplets which have a size less than said given magnitude flow with the drying gas into the drying chamber.
 2. In a method as recited in claim 1 and including the step of removing from said wall those droplets which strike thereagainst and cling thereto.
 3. In a method as recited in claim 2 and wherein the removal of the slurry from the wall is carried out by rotating the wall at a relatively slow speed with respect to a stationary scraper which scrapes the slurry from the wall.
 4. In a method as recited in claim 1 and wherein the step of spraying the slurry toward the wall is carried out by rotating at high speed an atomizer to which the slurry is fed to be sprayed by the atomizer toward the wall.
 5. In a method as recited in claim 2 and including the step of again preparing the slurry removed from the wall for spraying into the drying chamber and then again spraying the thus-prepared slurry toward the wall.
 6. In a method as recited in claim 1 and including the step of receiving dry material from the drying chamber on a moving discharge wall which delivers the dry material from the drying chamber.
 7. In a method as recited in claim 1 and wherein the drying gas stream is introduced in a laminar flow into the drying chamber across the sprayed slurried droplets so that at the location where the latter encounter the entering gas stream the stream is free of any non-linear currents.
 8. In an apparatus for drying pulpy slurries, a drying tower having upper and lower end regions and having a hollow interior drying chamber extending between said upper and lower end regions, spray means for spraying the pulpy slurry which is to be dried in the form of droplets horizontally across part of the drying chamber at the lower end region of the tower, conduit means communicating with the drying chamber at the lower end region of the tower for directing upwardly into the drying chamber a drying gas which travels upwardly across the horizontally sprayed droplets to carry droplets which are smaller than a given magnitude upwardly into the drying chamber to be dried during concurrent flow with the drying gas, and gas-flow smoothing means situated in the path of flow of the drying gas into the drying chamber below and adjacent the space through which the droplets are sprayed by the spray means for providing a laminar flow of the drying gas at the location where the latter encounters the sprayed droplets.
 9. The combination of claim 8 and wherein said gas-flow smoothing means includes a plurality of apertured plates situated one above the other and extending across the gas stream with the latter flowing through apertures of the plates to achieve the laminar gas flow.
 10. The combination of claim 8 and wherein a service room is situated beneath the lower end region of the tower, drive means operatively connected with said spray means for driving the latter, said drive means being situated in said service room, and said conduit means extending spirally around said service room up to the lower end region of the tower into communication with the drying chamber so that said conduit means has a lower portion situated on one side of the service room, said service room being formed with an entrance diametrically opposed to said lower portion of said conduit means.
 11. The combination of claim 8 and wherein a drive means is operatively connected to said spray means for rotating the latter about a vertical axis, to spray the droplets in a substantially horizontal plane which is normal to said vertical axis, and rotary wall means surrounding said vertical axis and spaced from said spray means to define with the latter a space between said wall means and spray means through which the drying gas flows upwardly into the drying chamber, whereby particles which are greateR than said magnitude strike against and cling to said rotary wall means.
 12. The combination of claim 11 and wherein a stationary scraper means extends axially along said rotary wall means adjacent an inner surface thereof which is directed toward said spray means for scraping from said rotary wall means those droplets which cling to said rotary wall means, and collecting means situated in the path of movement of the non-dried material scraped from said rotary wall means to receive the non-dried material.
 13. The combination of claim 11 and wherein a horizontal annular discharge wall is fixed to said rotary wall at an outer surface of the latter which is directed away from said spray means to rotate with said rotary wall, said discharge wall being situated in the path of falling movement of dried particles which flow outwardly beyond the drying gas stream to fall onto and be collected by said discharge wall, stationary removing means situated adjacent the upper surface of said discharge wall for removing dried material therefrom as the discharge wall rotates together with said rotary wall, and collecting means situated in the path of movement of the removed dried material to receive and collect the latter.
 14. The combination of claim 8 and wherein said gas-flow smoothing means includes a pair of apertured plates situated one above the other and formed with apertures which provide a relatively low resistance to the flow of drying gas on the order of five millimeters of water column pressure, said apertured plates distributing the drying gas uniformly with respect to the space through which the drying gas enters into the drying chamber and across which the particles are sprayed by said spray means.
 15. The combination of claim 14 and wherein a service room is situated beneath said lower end region of said tower, said conduit means extending spirally around said service room from a lower region of said conduit means situated at a lower part of said service room up to an upper region of said conduit means which is of an annular configuration and which is covered by said apertured plates, the latter surrounding an upper region of the service room, and said service room having an entrance situated at the elevation of the lower region of said conduit means.
 16. The combination of claim 11 and wherein a drive means is operatively connected to said rotary wall means for rotating the latter, said drive means being carried by said tower at said upper end region thereof and including a shaft extending downwardly along and through the drying chamber from said upper end region of the tower, said shaft having a lower portion operatively connected with and carrying said rotary wall means so that the latter rotates with said shaft, said drive means including at the upper end region of said tower a drive connected to said shaft of said drive means for rotating said shaft.
 17. The combination of claim 11 and wherein a drive means is operatively connected to said rotary wall means for rotating the latter, said drive means being situated at the elevation of the horizontally sprayed particles and including a driving motor carried by but situated at the exterior of the tower. 